BRZ as daily driver?

[UAM]

This car will be the company DD car. We will take the z34 and E90 and weekend cars.

[DEC1]

Originally Posted by Pakjk89

Great. Thanks for the info guys. I was mainly concerned because my parents don't want me to drive a rwd car as a daily driver and I wanted some input on whether their concern was a legit one. I know I should be concerned with bad weather but I figured a good pair of snow tires should do. Agreed?

Not a PAIR...you need all 4 snow tires! I've been driving RWD and FWD in New England with Blizzaks for years...the difference in snow and ice is absolutely amazing...best way is to get your snows mounted on a diff set of wheels and change 'em yourself....no wheel damage from changing summers to winters and back again every year.
But as all these guys mentioned...it's a lot more about HOW you drive than WHAT you drive.

[Draco-REX]

Originally Posted by DEC1

Not a PAIR...you need all 4 snow tires! I've been driving RWD and FWD in New England with Blizzaks for years...the difference in snow and ice is absolutely amazing...best way is to get your snows mounted on a diff set of wheels and change 'em yourself....no wheel damage from changing summers to winters and back again every year.
But as all these guys mentioned...it's a lot more about HOW you drive than WHAT you drive.

This.

You want 4 snows or you're just going to go straight. It seems a bit more expensive, but look at it this way; if you swap between two sets of tires, you tires will last twice as long. Additionally, because you have a set for summer and a set for winter, you can get dedicated summer tires (better than the Prius ones) and dedicated winter tires. This gives you the best of both worlds.

[fatoni]

Originally Posted by Corey

The engine's power is actually entirely irrelevant as long as it can provide enough power to use 100% of the tires' traction during perfectly straight forward acceleration. Note that this is very often not the case, as in my own car which is on wide sticky tires with only a meager 150hp. That "actual" grip circle for such a car would look smushed on top because the engine simply can't produce enough power to use much of the tire's potential forward grip.

What you're saying is exactly what one would expect, but the truth is tires are not so simple. Let me illustrate it this way:



The red lines I've drawn in illustrate what you'd guess represents a tire's grip: a linear relationship between lateral and longitudinal grip. This would represent a car that can either accelerate/brake at 100% without cornering, corner at 100% without accelerating/braking, or do some combination of the two in which the two forces always add up to 100%, i.e. 50% acceleration and 50% left cornering. This is not how tires work.

You can see there is overlap between between the "expected" lines and the actual grip circle at the four extreme forces. At those four points the maximum potential of the tire is the same. The interesting parts are the diagonal areas that represent a combination of lateral and longitudinal forces. The area within the circle but outside the "expected" lines represent the higher potential grip of the tire when combining forces. At any point in that area up until the outer limit of the grip circle you are using more of the tire's potential, and will thus produce faster lap times, than someone who operates only within the "expected" lines. Indeed, the combination of forces in those areas will add up to a greater net force than the maximum the tire can produce in any one direction. In other words using techniques like trail braking that use both lateral and longitudinal grip at the same time will produce more grip, and thus better lap times than someone who only "does one thing at a time."

i dont think its fair to say that its power is irrelevant provided there is enough. and my next point i admit i explained poorly. i didnt mean using half of what is expected purely cornering or purely accelerating. i meant that out of the grip available, you are spending it doing two things equally. you arent making any more grip that way, thats why its a circle. every point on that circle is equidistant. any line to any point on the perimeter of the circle is the same exact distance.

[Corey]

Originally Posted by fatoni

i dont think its fair to say that its power is irrelevant provided there is enough. and my next point i admit i explained poorly. i didnt mean using half of what is expected purely cornering or purely accelerating. i meant that out of the grip available, you are spending it doing two things equally. you arent making any more grip that way, thats why its a circle. every point on that circle is equidistant. any line to any point on the perimeter of the circle is the same exact distance.

I understand what you're trying to say and I will do my best to try and clear up some confusion. I apologize in advance if my terminology is incorrect, I'm not in the technical fields. Indeed you are right, the distance from the center of the graph, representing zero force in any direction, to any given point on the perimeter of the grip circle is equal. The radius of the circle is then a vector that represents the maximum grip of a tire (the vector's magnitude) in any one direction (the vector's direction). If you could instantly point the entire car in any desired direction without any steering this vector alone would represent the maximum total grip of a given tire (lateral grip is taken out of the picture).

Because that is not possible however, a tire's grip must be represented as a combination of two vectors, lateral and longitudinal force. It works in two directions to achieve acceleration in any area of the diagram that doesn't fall on either the X or Y axis. The differentiation here is I think where you are getting confused. Let's add some strictly hypothetical numbers to the illustration and take another look.



The easiest places to calculate are, again, where the circle crosses the X or Y axes. In our hypothetical graph at these points representing the tire's maximum lateral or longitudinal force it is producing 1.0 g of grip in a single direction for a net total of 1.0 g. For our example let's look at right cornering; if using all of the tire's grip to corner to the right then it will produce 1.0 g of grip before it begins to slide. I think we're both on the same page at this point.

Now let's look at the more interesting areas that represent combined forces again. The green vector represents the maximum grip of the tire if tires generated force in only one direction; the direction you wish to go, implying the car is already pointed in the proper direction as explained earlier. We know that is not the case however, so instead we have to look at grip as a combination of lateral and longitudinal forces. In our example case this means 0.66 g of right cornering force and 0.75 g of acceleration force simultaneously.

Now let's look at both of the above examples together, accelerating straight ahead and accelerating while cornering. In the first case, right cornering as fast as possible, the tires are producing 1.0 g of force to turn the car to the right. If given any longitudinal (braking or acceleration) force at all the tires will slip. In our second example however the tires are only using 0.66 g of force to corner to the right. In overly simple words example two is cornering 33% slower than example one. The catch is that because only 0.66 g of the tire's lateral grip is being used there is some room to add longitudinal grip before the tires begin to slide, and this is where things get really interesting. As shown in the illustration while cornering to the right at 0.66 g, or 66% of the theoretical maximum lateral acceleration, the tire can still produce up to 0.75 g of longitudinal grip, 75% of its maximum. That's a total of 0.66 + 0.75 = 1.41 g of grip (vs 1.0 g when using all of the tire's grip to corner), and that's quite impressive if you ask me.

What's it mean in the real world? Someone using 100% of their tires' grip for lateral acceleration WILL corner faster, there is no question about that. For a given radius corner the more lateral grip the tires produce, the higher the speed you can take the corner at without sliding. However, by using less grip to corner you can open up a lot of potential grip to use to brake or accelerate. In practical terms that means someone who goes by the "golden rule" of only doing one thing at a time will brake down to the maximum speed they can take the corner at, complete the turn at that constant speed, then begin to accelerate only after completing the turn. Remember, when cornering at the tire's maximum potential lateral grip any longitudinal force input will cause the tires to slide. Someone making the most of their tires however would brake down to a slower speed than the first driver (because they will be using less lateral grip) by first braking in a straight line then transitioning into trail braking (braking and cornering) towards the corner's apex, then begin to accelerate towards the corner's exit while completing the turn (accelerating and cornering). The result is while the first driver would enter the corner faster, the second driver would exit the corner faster and that advantage would be carried all the way to the next corner, resulting in better lap times for the driver who better used their tires. As it turns out this is exactly what you would observe in professional racing.

Of course there is a caveat though, and this is where power comes in. If the engine can't produce the power necessary to accelerate the car to a higher speed than the person using 100% of their grip to corner in the time it takes to exit the corner then you will still come out of the corner slower, and you will have lost time by entering slower too just to make matters worse. This is a very real phenomenon in some types of racing (cough Miatas cough) and represents how drivers have to adapt different styles of driving to different types of cars. Watching a very powerful car you could expect to see late, slow corner entries that get most of the turning done very early so the driver can get back on the gas as early as possible. A Miata on the other hand would seem to follow the "one thing at a time" strategy more closely because they just don't have the power to make up the early loss in entry speed before the corner exit.

I hope that is a bit more clear

[fatoni]

Originally Posted by Corey

I understand what you're trying to say and I will do my best to try and clear up some confusion. I apologize in advance if my terminology is incorrect, I'm not in the technical fields. Indeed you are right, the distance from the center of the graph, representing zero force in any direction, to any given point on the perimeter of the grip circle is equal. The radius of the circle is then a vector that represents the maximum grip of a tire (the vector's magnitude) in any one direction (the vector's direction). If you could instantly point the entire car in any desired direction without any steering this vector alone would represent the maximum total grip of a given tire (lateral grip is taken out of the picture).

Because that is not possible however, a tire's grip must be represented as a combination of two vectors, lateral and longitudinal force. It works in two directions to achieve acceleration in any area of the diagram that doesn't fall on either the X or Y axis. The differentiation here is I think where you are getting confused. Let's add some strictly hypothetical numbers to the illustration and take another look.



The easiest places to calculate are, again, where the circle crosses the X or Y axes. In our hypothetical graph at these points representing the tire's maximum lateral or longitudinal force it is producing 1.0 g of grip in a single direction for a net total of 1.0 g. For our example let's look at right cornering; if using all of the tire's grip to corner to the right then it will produce 1.0 g of grip before it begins to slide. I think we're both on the same page at this point.

Now let's look at the more interesting areas that represent combined forces again. The green vector represents the maximum grip of the tire if tires generated force in only one direction; the direction you wish to go, implying the car is already pointed in the proper direction as explained earlier. We know that is not the case however, so instead we have to look at grip as a combination of lateral and longitudinal forces. In our example case this means 0.66 g of right cornering force and 0.75 g of acceleration force simultaneously.

Now let's look at both of the above examples together, accelerating straight ahead and accelerating while cornering. In the first case, right cornering as fast as possible, the tires are producing 1.0 g of force to turn the car to the right. If given any longitudinal (braking or acceleration) force at all the tires will slip. In our second example however the tires are only using 0.66 g of force to corner to the right. In overly simple words example two is cornering 33% slower than example one. The catch is that because only 0.66 g of the tire's lateral grip is being used there is some room to add longitudinal grip before the tires begin to slide, and this is where things get really interesting. As shown in the illustration while cornering to the right at 0.66 g, or 66% of the theoretical maximum lateral acceleration, the tire can still produce up to 0.75 g of longitudinal grip, 75% of its maximum. That's a total of 0.66 + 0.75 = 1.41 g of grip (vs 1.0 g when using all of the tire's grip to corner), and that's quite impressive if you ask me.

What's it mean in the real world? Someone using 100% of their tires' grip for lateral acceleration WILL corner faster, there is no question about that. For a given radius corner the more lateral grip the tires produce, the higher the speed you can take the corner at without sliding. However, by using less grip to corner you can open up a lot of potential grip to use to brake or accelerate. In practical terms that means someone who goes by the "golden rule" of only doing one thing at a time will brake down to the maximum speed they can take the corner at, complete the turn at that constant speed, then begin to accelerate only after completing the turn. Remember, when cornering at the tire's maximum potential lateral grip any longitudinal force input will cause the tires to slide. Someone making the most of their tires however would brake down to a slower speed than the first driver (because they will be using less lateral grip) by first braking in a straight line then transitioning into trail braking (braking and cornering) towards the corner's apex, then begin to accelerate towards the corner's exit while completing the turn (accelerating and cornering). The result is while the first driver would enter the corner faster, the second driver would exit the corner faster and that advantage would be carried all the way to the next corner, resulting in better lap times for the driver who better used their tires. As it turns out this is exactly what you would observe in professional racing.

Of course there is a caveat though, and this is where power comes in. If the engine can't produce the power necessary to accelerate the car to a higher speed than the person using 100% of their grip to corner in the time it takes to exit the corner then you will still come out of the corner slower, and you will have lost time by entering slower too just to make matters worse. This is a very real phenomenon in some types of racing (cough Miatas cough) and represents how drivers have to adapt different styles of driving to different types of cars. Watching a very powerful car you could expect to see late, slow corner entries that get most of the turning done very early so the driver can get back on the gas as early as possible. A Miata on the other hand would seem to follow the "one thing at a time" strategy more closely because they just don't have the power to make up the early loss in entry speed before the corner exit.

I hope that is a bit more clear

thats not the case with the force being applied to the tire. its a vector and you cant even measure the individual acceleration and cornering forces. on that circle in your example you are producing 1g everywhere. thats why its a circle. when you add vectors or moments or whatever we are calling these, you dont just add the sides of the triangle, the sum of them is equal to the hypotenuse.

[Corey]

Originally Posted by fatoni

thats not the case with the force being applied to the tire. its a vector and you cant even measure the individual acceleration and cornering forces. on that circle in your example you are producing 1g everywhere. thats why its a circle. when you add vectors or moments or whatever we are calling these, you dont just add the sides of the triangle, the sum of them is equal to the hypotenuse.

You are right and wrong.

You are right that yes, you are producing 1 g all over the circle. The difference is how you produce that 1 g. As my examples above demonstrate, you get more use of your tires, and thus better lap times, by combining forces on the tires. If you datalog with an accelerometer (you absolutely can measure individual forces) and a good driver you will notice they can follow the perimeter of the circle quite closely. Here is a real example from Dennis Grant (http://farnorthracing.com/):

Originally Posted by Dennis Grant

This is actual accelerometer data for my car on run 12 of the 2004 Peru Pro, plotted XY in order to produce a Grip Circle. Here you can see the "squashed" nature of a live Grip Circle, plus the graph has a "stem" on the positive Y axis because it takes a very high horsepower car to "fill in the corners". But the circle is clearly visible.

Anyway since my explanations appear to be lacking I encourage you to read further on the subject elsewhere. Here's some good links.

'Driving the Circle' http://forum.wscc.co.uk/forum/index....ng-the-circle/
Dennis Grant's 'Autocross to Win' http://farnorthracing.com/autocross_secrets3_5.html
And this book is a good read that goes into a lot of the basics of racing such as the grip circle as well: http://www.amazon.com/Going-Faster-M...1796785&sr=8-1

[fatoni]

Originally Posted by Corey

You are right and wrong.

You are right that yes, you are producing 1 g all over the circle. The difference is how you produce that 1 g. As my examples above demonstrate, you get more use of your tires, and thus better lap times, by combining forces on the tires. If you datalog with an accelerometer (you absolutely can measure individual forces) and a good driver you will notice they can follow the perimeter of the circle quite closely. Here is a real example from Dennis Grant (http://farnorthracing.com/):





Anyway since my explanations appear to be lacking I encourage you to read further on the subject elsewhere. Here's some good links.

'Driving the Circle' http://forum.wscc.co.uk/forum/index....ng-the-circle/
Dennis Grant's 'Autocross to Win' http://farnorthracing.com/autocross_secrets3_5.html
And this book is a good read that goes into a lot of the basics of racing such as the grip circle as well: http://www.amazon.com/Going-Faster-M...1796785&sr=8-1

those arguments dont counter my point. you cant judge the net force by its parts. if you could then do you agree that drivers should brake while they accelerate? if you use 100% throttle and 100% braking you are still within the circle and you have 200% grip. i spent the last half of my shift discussing this with physicists yesterday and they dont seem to see it the way you do

[bestwheelbase]

It almost looks like a heart shape.

I will be mentally plotting these data points when I drive to work and run errands and take spirited jaunts in the countryside and get my car filthy and daily drive the hell out of it.

[Corey]

Originally Posted by fatoni

those arguments dont counter my point. you cant judge the net force by its parts. if you could then do you agree that drivers should brake while they accelerate? if you use 100% throttle and 100% braking you are still within the circle and you have 200% grip. i spent the last half of my shift discussing this with physicists yesterday and they dont seem to see it the way you do

You probably just aren't explaining it to them clearly. If you use 100% throttle and 100% braking you probably won't be moving at all, nevermind generating a significant amount of force on the tires. Both of those forces are on the Y axis and you'd end up somewhere right around 0,0 on the grip circle. Ideally you want to stay on the edge of the circle so as you can imagine that isn't quite ideal. This ties into why power is not that important (you can see the limit of its importance in the plot above; to fill in the gaps in the top of the plot). The forces your car is capable of producing through huge brakes, massive power, etc. is largely irrelevant if you can't convey it to the road surface through the tires. The grip circle is a graphical representation of forces produced by the tires, not by the engine, brakes, or otherwise.

[fatoni]

Originally Posted by Corey

You probably just aren't explaining it to them clearly. If you use 100% throttle and 100% braking you probably won't be moving at all, nevermind generating a significant amount of force on the tires. Both of those forces are on the Y axis and you'd end up somewhere right around 0,0 on the grip circle. Ideally you want to stay on the edge of the circle so as you can imagine that isn't quite ideal. This ties into why power is not that important (you can see the limit of its importance in the plot above; to fill in the gaps in the top of the plot). The forces your car is capable of producing through huge brakes, massive power, etc. is largely irrelevant if you can't convey it to the road surface through the tires. The grip circle is a graphical representation of forces produced by the tires, not by the engine, brakes, or otherwise.

not only did i explain it, i showed them this thread. i know what happens when you brake and gas at the same time. thats my point. you cant just go adding the forces the isolated forces like that. its not how that works. 1g is 1g. 1g isnt 1.6gs. that data shows that power is important simply because without it you arent at the edge of grip anytime that car is accelerating. i think we are kind of in agreement and to be honest am surprised this has stayed pretty civil. the bottom line is that a tire only has so much grip in any given set of conditions. no matter how much force you try to exceed grip is fixed by the shape of the circle. cornering and accelerating doesnt magically change that. you cant judge a net vector by its constituent parts. im chalking it up to miscommunication but combining forces isnt making more grip. its just the thing to do at a particular place on a particular race track

[serialk11r]

I haven't really thought much about this, but isn't there something missing from the "grip circle"? That is, depending on the weight distribution of the car, the tires are loaded unevenly, not to mention the tires are affected by suspension changes and stuff...

[Margovincent_22x]

Will changing Tires to a High Grip Tires cause problems for the electronic GAGETS inside the car example: VSC

[fatoni]

Originally Posted by serialk11r

I haven't really thought much about this, but isn't there something missing from the "grip circle"? That is, depending on the weight distribution of the car, the tires are loaded unevenly, not to mention the tires are affected by suspension changes and stuff...

yes and there are more factors (like speed, road conditions, temp etc.)than that but its a basic principle so its not really discussed when talking about the principles simply. i think the point is to teach novice drivers to use the most amount of grip available to achieve lower lap times. if you refer to the amount of grip in absolute numbers its complex, if you refer to them as percentages than it gets easier to understand. the suspension changes usually have an effect how much energy is required as you approach that 100% limit

Originally Posted by Margovincent_22x

Will changing Tires to a High Grip Tires cause problems for the electronic GAGETS inside the car example: VSC

i dont think tires alone would change how those work. just at which limits or speeds they work. i dont really know about that stuff though